Abstract:

A burner includes a primary air-coal mixture duct coaxially extended
through a secondary air wind box, a pulverized coal separator supported
within the primary air-coal mixture duct, a secondary air duct including
an inner secondary air duct and an outer secondary air duct coaxially
formed around the primary air-coal mixture duct, a primary air-coal
mixture conical outlet coupled with the outlet of the primary air-coal
mixture duct, and inner secondary air and outer conical outlets coupled
with the outlets of the inner secondary air and outer secondary air ducts
respectively. The conical outlets are arranged to delay the mixing time
of the primary air-coal mixture and secondary air flows through the
primary air-coal mixture and secondary air ducts and to prolong the
residence time in the center recirculation zone under the reduction
ability so as to effectively reduce the formation of NOx.

Claims:

1. A low NOx swirl coal combustion burner, comprising:a primary air-coal
mixture duct;one or more pulverized coal separators supported within said
primary air-coal mixture duct, wherein an outlet of the pulverized coal
separator, which is an opening having a smaller diameter, is alignedly
pointing towards an outlet of said primary air-coal mixture duct;a
secondary air wind box, wherein said primary air-coal mixture duct is
coaxially extended through said secondary air wind box; andan inner
secondary air vane, wherein inner and outer tubular sleeves are
encirclingly coupled with said primary air-coal mixture duct to form an
inner secondary air duct and an outer secondary air duct within the
secondary air wind box, wherein said inner secondary air vane is
supported within said inner secondary air duct;a primary air-coal mixture
conical outlet, wherein an opening of said primary air-coal mixture
conical outlet, with a smaller diameter, is coupled with said outlet of
said primary air-coal mixture duct;an inner secondary air conical outlet,
wherein an opening of said inner secondary air conical outlet, with a
smaller diameter, is coupled with an outlet of said inner secondary air
duct; andan outer secondary air conical outlet, wherein an opening of
said outer secondary air conical outlet, with a smaller diameter, is
coupled with an outlet of said outer secondary air duct.

2. The low NOx swirl coal combustion burner, as recited in claim 1,
wherein said pulverized coal separators are coaxially supported within
said primary air-coal mixture duct along a centerline thereof, wherein
the diameters of said pulverized coal separators are gradually and
sequentially reducing towards said outlet of said primary air-coal
mixture duct.

3. The low NOx swirl coal combustion burner, as in claim 1 or 2, wherein
said inner secondary air duct and said outer secondary air duct are
coaxially formed with respect to said primary air-coal mixture duct such
that said inner secondary air duct, an outer secondary air duct, and said
primary air-coal mixture duct share a common axis.

4. The low NOx swirl coal combustion burner, as recited in claim 1,
wherein said primary air-coal mixture conical outlet is extended
inclinedly at an angle α with respect to a centerline of said
primary air-coal mixture duct, wherein said inner secondary air conical
outlet is extended inclinedly at an angle β with respect to said
centerline of said primary air-coal mixture duct, wherein said outer
secondary air conical outlet is extended inclinedly at an angle γ
with respect to said centerline K of said primary air-coal mixture duct,
wherein said angles α, β, γ are the same, wherein each
of said angles α, β, γ has a threshold between
15.degree. to 35.degree..

5. The low NOx swirl coal combustion burner, as recited in claim 1,
wherein said inner secondary air vane comprises a set of curved vane
blades evenly, radially, and outwardly extended from an outer
circumferential wall of said primary air-coal mixture duct that a
corresponding edge of each of said curved vane blades is securely affixed
to said outer circumferential wall of said primary air-coal mixture duct.

6. The low NOx swirl coal combustion burner, as in claim 1, 2, or 4,
further comprising an inner secondary air damper supported at an inlet of
said inner secondary air duct.

7. The low NOx swirl coal combustion burner, as recited in claim 1,
further comprising an outer secondary air vane supported at an inlet of
said outer secondary air duct.

8. The low NOx swirl coal combustion burner, as recited in claim 7,
wherein said outer secondary air vane comprises a set of flat vane blades
and a regulator, wherein each of said flat vane blades is coupled at an
inlet wall of said outer secondary air duct via said regulator.

Description:

BACKGROUND OF THE PRESENT INVENTION

[0001]1. Field of Invention

[0002]The present invention relates to a burner, and more specifically to
a centrally fuel rich (CFR) swirl coal combustion burner which can reduce
the output of the emissions amount of NOx.

[0003]2. Description of Related Arts

[0004]Nitrogen Oxide (NOx) is one of the main contaminants for air
pollution. It not only forms the acid rain to damage the ecological
environment, but also forms the actinic fog to harm the health of human
being. The coal combustion is one of the main sources of the generation
of nitrogen oxide compound. At the present, there are two methods to
control the formation of NOx. The first method is low NOx combustion
technology which can reduce the formation of NOx. The second method is
the flue gas denitrification which applies removing reactant of
denitrification to the flue gas to remove NOx. China Patent, CN1207511C,
publication date of Jun. 22, 2005, entitled "Centrally Fuel Rich (CFR)
Swirl Coal Combustion burner", teaches the control of the formation of
NOx, as the first method, to control the formation of NOx. Accordingly,
the burner comprises a pulverized separator having a cone shape to
collect the pulverized coal at the central portion of a primary air-coal
mixture duct, wherein the injection of the pulverized coal is aligned
with a center of the central recirculation zone of the burner. Throughout
the combustion of the pulverized coal, the concentration of the
pulverized coal is increased within the central recirculation zone while
the residence time of pulverized coal is prolonged to reduce the
formation of NOx. However, there is no conical outlet installed at the
outlets of the primary air-coal mixture, inner and outer secondary air
ducts, the pulverized coal at the primary air-coal mixture and inner and
outer secondary air ducts is parallelly spurted into the furnace so that
the central recirculation zone formed by the swirl of the secondary air
is relatively small. Thus, the residence time of pulverized coal in the
central recirculation is not long enough to inhibit the formation of
nitrogen oxide compound at most. Also, without the conical outlet, the
air through the primary air-coal mixture and secondary air ducts is mixed
immediately into the furnace, so that the ability of NOx reduction is
substantially decreased. Therefore, it cannot effectively inhibit the
formation of NOx. Furthermore, the major drawbacks of the second method
of controlling the nitrogen oxide compound, through the flue gas
denitrification by applying removing reactant of denitrification to flue
gas to remove nitrogen oxide compound, are high investment cost and
operating cost.

SUMMARY OF THE PRESENT INVENTION

[0005]A main object of the present invention is to provide a low NOx swirl
coal combustion burner, which can solve the problem of the conventional
CFR swirl coal combustion burner being ineffectively inhibited the
formation of fuel-NOx.

[0006]Accordingly, in order to accomplish the above objects, the present
invention provides a low NOx swirl coal combustion burner comprises a
primary air-coal mixture duct, a conical pulverized coal separator, a
secondary air wind box, and an inner secondary air vane, wherein the
primary air-coal mixture duct is coaxially extended through the secondary
air wind box. The pulverized coal separator is supported within the
primary air-coal mixture duct, wherein an outlet of the pulverized coal
separator, having a smaller diameter, is alignedly pointing towards an
outlet of the of primary air-coal mixture duct. Inner and outer tubular
sleeves are encirclingly coupled with the primary air-coal mixture duct
to form an inner secondary air duct and an outer secondary air duct
within the secondary air wind box. The present invention further
comprises a primary air-coal mixture conical outlet, an inner secondary
air conical outlet, and an outer secondary air conical outlet. The
opening of the primary air-coal mixture conical outlet, with a smaller
diameter, is coupled with the outlet of the primary air-coal mixture
duct. The opening of the inner secondary air conical outlet, with a
smaller diameter, is coupled with the outlet of the inner secondary air
duct. The opening of the outer secondary air conical outlet, with a
smaller diameter, is coupled with the outlet of the outer secondary air
duct.

[0007]Accordingly, the present invention achieves the following
advantages.

[0008]The secondary air flow is partitioned into two portions into the
furnace through the inner and outer secondary air ducts, wherein the
inner and outer secondary air vanes are arranged to regulate the two
portions of the secondary air flow in a swirling manner at the inner
secondary air duct and the outer secondary air duct respectively. Under
the effects of the primary air-coal mixture conical outlet, the inner
secondary air conical outlet, and the outer secondary air conical outlet,
the flow of air-coal mixture at the primary air-coal mixture duct is
mixed with the swirling air flow at the inner and outer secondary air
ducts to form a moderate central recirculation zone. In addition, the
burner of the present invention does not include any central duct. The
primary air-coal mixture duct is located at a center of the burner,
wherein the primary air-coal mixture flow is formed in a non-swirling
manner that the primary air-coal mixture flow is straight-forwardly
passing through the primary air-coal mixture duct. One or more pulverized
coal separators are coaxially supported within the primary air-coal
mixture duct along the centerline thereof to inject the flow of air-coal
mixture at the center of primary air-coal mixture duct into the furnace,
so as to increase the amount of the pulverized coal at the central
recirculation zone, to enhance the reduction ability of the air-coal
mixture at the central recirculation zone, and to prolong the residence
time of the air-coal mixture at the center recirculation zone for
effectively reducing the formation of NOx. The conical outlets are
arranged to delay the mixing time of the primary air-coal mixture and
secondary air flows through the primary air-coal mixture and inner and
outer secondary air ducts and to further prolong the residence time in
the center recirculation zone under the reduction ability so as to
effectively reduce the formation of NOx. Accordingly, the secondary air
flow is partitioned into two portions for being transversely injected
into the furnace. The inner portion of the secondary air flow is used as
an igniter for igniting the pulverized coal. The outer portion of the
secondary air flow is used as an oxygen suppler for supplying enough
oxygen for complete combustion of the pulverized coal, so as to inhibit
the formation of NOx. The staged mixing manner of the secondary air flow
at the radial direction has an advantage of reducing the emission of NOx.

[0009]These and other objectives, features, and advantages of the present
invention will become apparent from the following detailed description,
the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a sectional view of a low NOx swirl coal combustion burner
according to a preferred embodiment of the present invention, wherein an
outer secondary air vane is omitted.

[0011]FIG. 2 is the sectional view of the low NOx swirl coal combustion
burner according to the above preferred embodiment of the present
invention, illustrating the outer secondary air vane being installed.

[0012]FIG. 3 is a sectional view of a curved vane blade of the low NOx
swirl coal combustion burner according to the above preferred embodiment
of the present invention.

[0013]FIG. 4 is a top view of the curved vane blade the low NOx swirl coal
combustion burner according to the above preferred embodiment of the
present invention.

[0014]FIG. 5 is a sectional view of an outer secondary air vane according
to the above preferred embodiment of the present invention, illustrating
the structural relationship between the outer secondary air vane and the
outer secondary air duct.

[0015]FIG. 6 is a sectional view of the inner secondary air vane welded on
the wall of the primary air-coal mixture duct of the low NOx swirl coal
combustion burner according to the above preferred embodiment of the
present invention.

[0017]The primary air-coal mixture duct 1 is coaxially extended through
the secondary air wind box 3, wherein the pulverized coal separator 2 is
supported within the primary air-coal mixture duct 1. An outlet of the
pulverized coal separator 2, which is an opening having a smaller
diameter, is alignedly pointing towards an outlet of the primary air-coal
mixture duct 1. Inner and outer tubular sleeves 7, 8 are encirclingly
coupled with the primary air-coal mixture duct 1 to form an inner
secondary air duct 9 and an outer secondary air duct 10 within the
secondary air wind box 3. The inner secondary air vane 4 is supported
within the inner secondary air duct 9. The opening of the primary
air-coal mixture conical outlet 11, with a smaller diameter, is coupled
with the outlet of the primary air-coal mixture duct 1. The opening of
the inner secondary air conical outlet 12, with a smaller diameter, is
coupled with an outlet of the inner secondary air duct 9. The opening of
the outer secondary air conical outlet 13, with a smaller diameter, is
coupled with an outlet of the outer secondary air duct 10.

[0018]As shown in FIGS. 1 and 2, a set of pulverized coal separators 2 is
spacedly supported within primary air-coal mixture duct 1. In
particularly, the pulverized coal separators 2 are coaxially supported
within the primary air-coal mixture duct 1 along the centerline K. The
diameter of each of the pulverized coal separators 2 is gradually
reducing towards the outlet of the primary air-coal mixture duct 1 while
the diameters of the pulverized coal separators 2 are sequentially
reducing towards the outlet of the primary air-coal mixture duct 1.
Therefore, when the flow of the pulverized coal passes through the
pulverized coal separators 2 along the primary air-coal mixture duct 1, a
high-dense pulverized coal region is formed at the central portion of the
primary air-coal mixture duct 1 while a less-dense pulverized coal region
is formed near the inner wall of the primary air-coal mixture duct.

[0019]As shown in FIGS. 1 and 2, the inner secondary air duct 9 and the
outer secondary air duct 10 are coaxially formed with respect to the
primary air-coal mixture duct 1 such that the inner secondary air duct 9,
an outer secondary air duct 10, and the primary air-coal mixture duct 1
share a common axis. Accordingly, the coaxial configuration of the
primary air-coal mixture duct 1, the inner secondary air duct 9 and the
outer secondary air duct 10 enhances the circulation of the primary
air-coal mixture and secondary air flows passing therethrough.

[0020]As shown in FIGS. 1 and 2, the primary air-coal mixture conical
outlet 11 is extended inclinedly at an angle α with respect to the
centerline K of the primary air-coal mixture duct 1. The inner secondary
air conical outlet 12 is extended inclinedly at an angle β with
respect to the centerline K of the primary air-coal mixture duct 1. The
outer secondary air conical outlet 13 is extended inclinedly at an angle
γ with respect to the centerline K of the primary air-coal mixture
duct 1. Accordingly, the angles α, β, γ are the same,
wherein each of the angles α, β, γ has a threshold
between 15° to 35°. It is worth to mention that if the
angles α, β, γ are larger than the threshold, the air
divergent angle will be substantially increased to form an open airflow.
Therefore, pulverized coal will flow near to the water-cooling wall
region so as to cause the deterioration of combustion and the slagging at
the water-cooling wall. If the angles α, β, γ are
smaller than the threshold, the primary air-coal mixture conical outlet
11, the inner secondary air conical outlet 12, and the outer secondary
air conical outlet 13 will take no effect as the structure without the
conical outlet 11, the inner secondary air conical outlet 12, and the
outer secondary air conical outlet 13. In other words, the smaller angles
α, β, γ will incapable of forming a moderate central
recirculation zone and keeping a stable flame. Therefore, the angles
α, β, γ of the conical outlets 11, 12, 13 are set within
the threshold will have great influence on stabilizing the combustion and
forming the moderate central recirculation zone to reduce the emission
amount of NOx.

[0021]As shown in FIGS. 3, 4, and 6, the inner secondary air vane 4
comprises a set of curved vane blades 6, wherein each of the curved vane
blades 6 has a curved configuration. Accordingly, the curved vane blades
6 are evenly, radially, and outwardly extended from the outer
circumferential wall of the primary air-coal mixture duct 1 within the
inner secondary air duct 9. In particularly, the corresponding edge of
each of the curved vane blades 6 is securely affixed to the outer
circumferential wall of the primary air-coal mixture duct 1. Accordingly,
the structural configuration of the inner secondary air vane 4 has a
simple structure and is adapted to distribute uniform air flow.

[0022]As shown in FIGS. 1 and 2, the burner of the present invention
further comprises an inner secondary air damper 16 supported at an inlet
of the inner secondary air duct 9, wherein the opening valve of the inner
secondary air damper 16 is selectively adjusted to adjustably control the
amount of air flow passing through the inner secondary air duct 9 and the
outer secondary air duct 10. Accordingly, the air flow is guided to pass
through the inner secondary air duct 9 in a swirling manner while the air
flow is guided to straight-forwardly pass through the outer secondary air
duct 10 in a non-swirling manner. By selectively regulating the flow
ratio of the air flow between the inner secondary air duct 9 and the
outer secondary air duct 10 to adjust the swirl intensity of the air
flow, the magnitude of the central recirculation zone is adapted to be
adjustably controlled.

[0023]As shown in FIGS. 1, 2, and 5, the burner of the present invention
further comprises an outer secondary air vane 5 supported at an inlet of
the outer secondary air duct 10 to regulate the air flow passing through
the outer secondary air duct 10 in a swirling manner. Therefore, the air
flow is guided to pass through the inner secondary air duct 9 and the
outer secondary air duct 10 in a swirling manner. Accordingly, the swirl
intensity of the air flow is selectively adjusted by either selectively
adjusting a regulating angle of the outer secondary air vane 5 or
selectively adjusting a position of the outer secondary air vane 5 within
the outer secondary air duct 10, so as to adjustably control the
magnitude of the central recirculation zone.

[0024]As shown in FIGS. 2 and 5, the outer secondary air vane 5 comprises
a set of flat vane blades 14 and a regulator 15 to selectively adjust the
regulating angle of each of the flat vane blades 14. Accordingly, each of
the flat vane blades 14 has a straight planar configuration. Each of the
flat vane blades 14 is coupled at the inlet wall of the outer secondary
air duct 10 via the regulator 15. Accordingly, the structural
configuration of the outer secondary air vane 5 has a simple structure
and is easy to adjust the swirl intensity of the air flow at the outer
secondary air duct 10.

[0025]According to the preferred embodiment, the burner of the present
invention is incorporated with a 1025 ton per hour B&WB-1025/18.3-M type
boiler made by Babcock & Wilcox Beijing Co. Ltd, as an example. The
combustion condition is shown as: lean coal as the pulverized coal,
Vdaf=21.35%; Aar=29.42%; Mt=7.1%; and Q.sub.net,ar=23162
kJ/kg, wherein Vdaf is the volatile matter as dry ash free, Aar
is ash as received, Mt is the moisture as received, and Q.sub.net,ar
is the net heating value as received. By using 8 burners of the present
invention at the bottom row of burners on the boiler, the amount of NOx
emission is 1113 mg/m3 (6% of O2). In comparison with the same
type boiler without using the burners of the present invention, the
amount of NOx emission is 1206 mg/m3 (6% of O2). Therefore, a
decrease of 8% of the amount of NOx emission is determined by
incorporating the burner of the present invention with the boiler.

[0026]The burner of the present invention is incorporated with a 670 ton
per hour B&WB-670/13.7-M type boiler made by Babcock & Wilcox Beijing Co.
Ltd, as another example. The combustion condition is shown as: low-grade
coal as the pulverized coal, Vdaf=22.86%; Aar=35.28%;
Mt=7.4%; and Q.sub.net,ar=18130 kJ/kg, wherein Vdaf is the
volatile matter as dry ash free, Aar is ash as received, Mt is
the moisture as received, and Q.sub.net,ar is the net heating value as
received. By using 6 burners of the present invention at the bottom row
of burners on the boiler, the amount of NOx emission is 795 mg/m3
(6% of O2). In comparison with the same boiler without using the
burners of the present invention, the amount of NOx emission is 961
mg/m3 (6% of O2). Therefore, a decrease of 17.27% of the amount
of NOx emission is determined by incorporating the burner of the present
invention with the boiler.

[0027]The burner of the present invention is incorporated with a 1025 ton
per hour B&WB-1025/16.8-M type boiler made by Babcock & Wilcox Beijing
Co. Ltd, as another example. The combustion condition is shown as:
bituminous coal as the pulverized coal, Vdaf=33.15%;
Aar=27.13%; Mt=11.8%; and Q.sub.net,ar=17790 kJ/kg, wherein
Vdaf is the volatile matter as dry ash free, Aar is ash as
received, Mt is the moisture as received, and Q.sub.net,ar is the
net heating value as received. By using 8 burners of the present
invention at the bottom row of burners on the boiler, the amount of NOx
emission is 728 mg/m3 (6% of O2). In comparison with the same
boiler without using the burners of the present invention, the amount of
NOx emission is 843.55 mg/m3 (6% of O2). Therefore, a decrease
of 13.74% of the amount of NOx emission is determined by incorporating
the burner of the present invention with the boiler.

[0028]Accordingly, the operation of the burner of the present invention is
shown as the following. The flow of air-coal mixture is injected into the
furnace through the primary air-coal mixture duct 1, wherein the primary
air-coal mixture conical outlet 11 is coupled at the outlet of the
primary air-coal mixture duct 1 at a position close to the furnace. The
pulverized coal separator 2 is supported within the primary air-coal
mixture duct 1, wherein the diameter of the pulverized coal separator 2
is gradually reducing towards the outlet of the primary air-coal mixture
duct 1. In addition, the outlet of the pulverized coal separator 2, which
is the opening having a smaller diameter, is alignedly pointing towards
the furnace. After the flow of air-coal mixture passes through the
pulverized coal separator 2, the flow of air-coal mixture is partitioned
into two portions. The inner central portion of the flow of air-coal
mixture is the high-dense pulverized coal region while the outer
peripheral portion of the flow of air-coal mixture is the less-dense
pulverized coal region. The two portions of the flow of air-coal mixture
are injected into the furnace through the primary air-coal mixture
conical outlet 11. The secondary air flow passes through the secondary
air wind box 3 to the inner secondary air duct 9 and the outer secondary
air duct 10, wherein the secondary air flow is regulated to be swirled
along the inner secondary air duct 9 and the outer secondary air duct 10
via the inner air vane 4 and the outer secondary air vane 5 respectively.
It is worth to mention that the swirling direction of the secondary air
flow at the inner secondary air duct 9 is the same as the swirling
direction of the secondary air flow at the outer secondary air duct 10.
The secondary air flow is then injected into the furnace through the
inner secondary air conical outlet 12 and the outer secondary air conical
outlet 13. Therefore, a moderate central recirculation zone is formed
within the furnace to stabilize the combustion of the air-coal mixture.

[0029]One skilled in the art will understand that the embodiment of the
present invention as shown in the drawings and described above is
exemplary only and not intended to be limiting.

[0030]It will thus be seen that the objects of the present invention have
been fully and effectively accomplished. The embodiments have been shown
and described for the purposes of illustrating the functional and
structural principles of the present invention and is subject to change
without departure from such principles. Therefore, this invention
includes all modifications encompassed within the spirit and scope of the
following claims.